The men were dressed in police uniforms and fired more than 200 rounds before fleeing with Mintoo and four gangsters from the Nabha jail in Patiala district, reports said.

The 49-year-old Harminder Singh’s arrest in 2014 was hailed as a huge success for anti-terror operations in Punjab, which battled Sikh insurgency for almost three decades till early 1990s.

A police team was sent to the jail, where several militants were housed when the Sikh insurgency was at its peak.

Security has been stepped up and an alert sounded in Punjab and neighbouring states following the audacious jail break.

Singh and his aide Gurpreet Singh alias Gopi were arrested in November 2014 at the New Delhi airport on his arrival from Thailand. The two were tracked with the help of central intelligence agencies.

The KLF chief was wanted in at least 10 terror offences, Punjab’s top police officer Sumedh Singh Saini had said after his arrest. His aide Gopi was tasked with executing targeted killings of Hindu leaders in 2013, which the Punjab Police foiled.

Singh, said police, had spent time in Pakistan. The neighbouring country’s all-powerful spy agency the ISI had asked him to carry out a strike on Independence Day that year but the plan didn’t work, the Punjab Police had said.

The ISI has helped Khalistani outfits with money, arms and training.

Singh also sought funds from and Europe and North America-based sympathisers to raise his own outfit.

Born in Dalli village of Jalandhar district in April 1967, Harminder Singh, whose family shifted to Goa in 1980s, was using a fake Malaysian passport and documents to travel.

He also travelled to Cambodia, Laos and Myanmar, besides Thailand, where he set up a base.

The Khalistan Liberation Force was founded after the 1984 Operation Bluestar when the Indian Army stormed the holiest Sikh shrine the Golden Temple in Amritsar to flush out militants, triggering widespread anger.

The KLF remained among the most dreaded of the Sikh organisations fighting for a separate homeland of Khalistan till 1993 when several of its frontline militants were killed in a ruthless anti-terrorist campaign led by Punjab Police chief KPS Gill.